Combustors with improved dynamics

Abstract

A combustor comprises an outer combustor casing defining a plurality of circumferentially adjoining combustion chambers. Each combustion chamber comprises a dome at an upstream end and an outlet at a downstream end. A plurality of pre-mixers are joined to the combustor dome of each respective combustion chamber. The pre-mixers comprise a duct having an inlet at one end for receiving compressed air, an outlet at an opposite end disposed in flow communication with the combustion chamber and a swirler disposed in the duct adjacent the duct inlet for swirling air channeled therethrough. A fuel injector is provided for injecting fuel into the pre-mixer ducts and for mixing with the air in the ducts for flow into the combustion chamber to generate a combustion flame at the duct outlets. A portion of the pre-mixers comprise an altered flameholding capability so as to distribute the resulting combustion flames from the respective portion of the pre-mixers axially downstream with respect to the non-altered pre-mixers so as to reduce the dynamic pressure amplitude of the combustion flames.

What is claimed is:  
     
       1. A combustor comprising: 
       an outer combustor casing defining a plurality of circumferentially adjoining combustion chambers, each combustion chamber comprising a dome at an upstream end and an outlet at a downstream end;  
       a plurality of pre-mixers joined to said combustor dome of each respective combustion chamber, said pre-mixers comprising a duct having an inlet at one end for receiving compressed air, an outlet at an opposite end disposed in flow communication with said combustion chamber and a swirler disposed in said duct adjacent said duct inlet for swirling air channeled therethrough; and  
       a plurality of fuel injectors for injecting fuel into said pre-mixer ducts and for mixing with said air in said ducts for flow into said combustion chamber to generate combustion flames at said duct outlets;  
       wherein a portion of said pre-mixers comprise an altered flameholding capability so as to distribute said resulting combustion flames from said respective portion of said pre-mixers axially downstream with respect to a portion of non-altered pre-mixers to reduce the dynamic pressure amplitude of said combustion flames;  
       wherein said pre-mixers comprising an altered flameholding capability comprise at least one orifice for directing high velocity air to impinge upon said combustion flames so as to lift said respective combustion flames from said dome end and shift said combustion flames axially downstream.  
     
     
       2. A combustor, in accordance with claim  1 , wherein the velocity of said high velocity air is great enough to overcome the flame propagation speed. 
     
     
       3. A combustor, in accordance with claim  1 , wherein said high velocity air is supplied directly to said respective orifices from a high-pressure air source. 
     
     
       4. A combustor, in accordance with claim  3 , wherein said high velocity air supplied from said high-pressure air source is manipulated so as to tune said combustion chamber for minimum combustion instability. 
     
     
       5. A combustor, in accordance with claim  1 , wherein said high velocity air is supplied passively into said respective orifices by providing fluid communication between said respective orifices and a high-pressure region of a turbine engine. 
     
     
       6. A combustor, in accordance with claim  1 , wherein said combustion flames are shifted axially downstream so as to be axially positioned proximate a pressure node source to minimize Rayleigh's Criteria.